The present invention relates to compositions of matter for thermoplastic nanocomposites containing nanoscale carbon fibers and tubes.
One-dimensional, carbon-based, nano-structured materials are generally divided into three categories based on their diameter dimensions: (i) single-wall carbon nanotubes (SWNT, 0.7-3 nm); (ii) multi-wall carbon nanotubes (MWNT, 2-20 nm); (iii) carbon nanofibers (CNF, 40-100 nm). While the length of carbon nanofiber) ranges 30-100 μm, it is difficult to determine the lengths of SWNT and MWNT because of their strong proclivity to aggregate (to form “ropes”), but they are generally considered to be two-orders of magnitude shorter than CNF. In comparison to single-walled or multi-walled carbon nanotubes, vapor-grown carbon nanofibers are more attractive from the standpoint of practicality in terms of their relatively low cost and availability in larger quantities as the result of their more advanced stage in commercial production. These nanofibers are typically produced by a vapor-phase catalytic process in which a carbon-containing feedstock (e.g. CH4, C2H4 etc.) is pyrolyzed in the presence of small metal catalyst (e.g. ferrocene, Fe(CO)5 etc.) and have an outer diameter of 60-200 nm, a hollow core of 30-90 nm, and length on the order of 50-100 microns. It follows that having aspect ratios (length/diameter) of greater than 800 should make them useful as nano-level reinforcement for polymeric matrices. Furthermore, since their inherent electrical and thermal transport properties are also excellent, there are many possibilities imaginable for tailoring their polymer matrix composites into affordable, light-weight, multifunctional materials. Conceptually, there are three general techniques for dispersing chemically unmodified VGCNF in the polymer matrices: (1) melt blending (2) solution blending, and (3) reaction blending. For the reaction blending route, there are two scenarios: (a) in-situ polymerization of monomers (AB) or co-monomers (AA+BB) in the presence of dispersed VGCNF that occurs without forming any covalent bonding between the VGCNF and the matrix polymer, or (b) in-situ grafting of AB monomers that occurs with direct covalent bonds formed between the VGCNF and the matrix polymer. While melt-blending is perhaps the most cost effective approach to VGCNF-based nanocomposites, and has been applied to thermoplastic, thermosetting and elastomeric matrices, the resulting nano-composite materials are by and large less than optimal, especially in the cases where polymer-VGCNF incompatibility adversely impact the desired level of dispersion and the breakage of the carbon nanofibers by high shear forces reduce the reinforcing aspect ratios. The solution blending appears to have circumvented these problems, for example, the nanocomposite materials produced by this route have shown 2-3 orders of magnitude higher in electrical conductivity and much lower percolation threshold (<1 vol %) than similar materials prepared by the melt-blending route. To our knowledge, we are not aware of any report in the literature that describes successful preparation of VGCNF-based nanocomposite materials via reaction blending. However, similar non-grafting, reaction blending processes have been reported for unmodified SWNT and MWNTg In addition, there are reports on the grafting of a polymer either to or from a SWNT or MWNT that typically involved prior oxidation or functionalization of the CNT with a reactive group (e.g. surface-bound acid chloride or initiator for atom-transfer radical polymerization).
Using Friedel-Crafts acylation, Applicants were able to chemically attach meta-poly(etherketone) onto the surfaces of VGCNF, viz. forming direct bonds between the polymer grafts and VGCNF, via in-situ polymerization of m-phenoxybenzoic acid in the presence of VGCNF in poly(phosphoric acid).
Accordingly, it is an object of the present invention to provide new in-situ nanocomposites derived from carbon nanofibers and carbon multiwalled nanotubes.
It is another object of the present invention to provide a process for attaching a poly(ether-ketone) onto the surfaces of nanoscale carbon fibers and tubes.
Other objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.